1. Field of the Invention
The invention relates to a device enabling control of the communication of a plurality of electrically isolatable bus segments. Since each segment is generally connected to output terminals of circuits capable of emitting or receiving digital data, putting two or more segments into communication then makes it possible to exchange data between the circuits of one of the segments and the circuits of other segments.
2. Description of the Prior Art
Buses capable of being subdivided into a plurality of segments comprise an important application, in particular in computer central processing units (CPUs). In order for a plurality of functional subsystems of the unit to operate simultaneously and independently, it is necessary to be able to isolate the circuits of these subsystems. On the other hand, it is also necessary to put two functional subsystems into communication with one another. Examples of subsystems include operators, registers or banks of registers. For solving the above problem, one solution is to provide means with which bus segments can be isolated at will, each segments being connected to the circuits that comprise one functional subsystem.
To realize buses comprising a plurality of isolatable segments, controlled switches are used, one switch connecting two homologous lines of two adjacent segments. These switches are controlled by selection signals emitted by the control unit of the computer. The logical state of the selection signals thus defines a certain bus configuration. A plurality of segments can be connected in series, while others can be isolated totally.
It is not difficult to realize such buses when the number of segments is relatively low. Contrarily, if the possibilities for parallelism are to be increased, it is desirable to have buses that can be subdivided into numerous independent segments. It is also necessary to be able to put two or more of any of the segments into communication, which could lead to a situation where the total bus capacity is very high. In that case, means are needed with which the voltages of the signals transmitted can be maintained at a sufficient level over the entire length of the bus. To do this, each bus segment is associated with amplification means, which are actuated each time the segment operates in the emission, transmission, or reception mode.
It is then also necessary to provide control means, in particular amplification devices, with which correct functioning of this system can be attained. In particular, the actuation of the amplifier associated with one segment must be delayed with respect to that of the adjacent segment by way of which the data arrives. If this constraint were to be neglected, there would be the risk of creating a state of instability that could lead to anarchic function of the amplifiers.